An open-label, prospective evaluation of the efficacy of vitamin D supplementation starting 1 month before and continuing for the duration of combination therapy with pegylated interferon alpha (2a or 2b) plus ribavirin in patients with chronic viral hepatitis C genotype 1 or 4, nonresponders to a first antiviral therapy.Vitamin D supplementation is started one month before antiviral therapy in order to introduce pegylated interferon plus ribavirin in patients with optimal vitamin D status